DE1065552B - Process for the production of stoving enamels - Google Patents

Description

THE END

CHRIFT 1065 552

R 17837 IVc / 22 h

REGISTRATION DATE: November 25, 1955

NOTICE DEK REGISTRATION AND ISSUE OF THE FROM LE GE S CHRI FT:

September 17th, 1959

It is known that baking enamels with good properties can be obtained by using solutions of Condensation products from melamine and formaldehyde, their condensation in the presence of alcohols is done with solutions of alkyd resins modified with saturated and unsaturated fatty acids mixes. For this it is necessary to use the alkyd resins obtained in solid form during manufacture to be dissolved in aromatic solvents before mixing. The second mix component, the melamine resin, falls because of the condensation in the alcoholic medium during production in Aiko get resolved. In contrast, the modified alkyd resins that are suitable for a combination are in Alcohols alone are insoluble, so that they are predominantly used for the purpose of combination in a special operation aromatic solvents must be dissolved. Undissolved alkyd resins are essential for this mode of operation not suitable.

The condensation or etherification of a melamine-formaldehyde condensation product in the presence of alcohols is usually carried out in the so-called cycle in order to remove the water introduced with the formaldehyde and the water formed during the condensation or etherification of the methylolmelamine compounds; that is, the reaction kettle is equipped with a descending cooler and a closed receiver, which allows the almost exclusively used, butane process for the production of stoving enamels

Applicant:

Reichhold Chemie A. G., Hamburg-Wandsbek, Iversstrasse 57

Dr. rer. pole. Dr. A. Peter Kocb, Hamburg-Wandsbek, has been named as the inventor

not because the solvent used for them consists exclusively of alcohols. In order to enable the miscibility with undissolved alkyd resins, some of the alcohols would have to be replaced by good solvents for alkyd resins. This was primarily aromatic hydrocarbons are suitable, which also etherified melamine resins are well tolerated 25. According to the invention, part of the alcohol used is removed from alcohol-modified melamine resins in the course of their production process after the condensation has ended and replaced by aromatic solvents. The ratio of the dissipating primary alcohols from the overdistilled 30 turned alcohol to the aromatic solvents

To separate water. This is deducted from time to time while the iso- or n-Butanol continuously flows back into the reaction vessel. This circular distillation will eventually carried out in a vacuum so that certain temperatures are not exceeded in order to avoid the catheterized To conserve melamine-formaldehyde resins.

Furthermore, the resin content of solutions of etherified melamine resins at the end of the condensation is around 50 ^fl / o, while solutions with 60 or more percent resin are desirable. The concentration or distilling off of the iso- or n-butanol therefore immediately follows the actual condensation, so that condensation and concentration are to be understood as one operation. The freedom in the later selection of suitable solvents for the combination of melamine resins with alkyd resins is not bought at the cost of a special distillation process. It has now been found that baking enamels can be used

teln should be about 1: 1. At the same time, some of the n-butanol is replaced by the aromatics, which is undesirable in the amounts present in the starting solution in the subsequent synthetic resin varnish.

The choice of which to mix with etherified melamine resins. suitable alkyd resins is proportionate great. There are modified alkyd resins with a high, medium and low fatty acid content suitable. Unsaturated drying and semi-drying fatty acids are suitable for modification Alkyd resins with high and preferably medium oil content are selected. The saturated natural and synthetic fatty acids are used to obtain suitable alkyd resins with a low fatty acid content. The mixing ratio of melamine resin to alkyd resin can vary within wide limits will vary depending on the character of the alkyd resin, but the best results are known in the case of the use of 30 to 40 parts by weight of solid

obtained with particularly good properties when 50 melamine resin is obtained at 70 to 60 parts by weight of solvent-free modified alkyd resin corresponding to the solvent, mixed alcohol-modified melamine resins with solvent-free alkyd resins. The previously known method consists in the fact that, in addition to saving a melamine resin, a homogeneous mixture of the two is suitable for this combination of operations

909 628/391

Claims (1)

Resin components is achieved and the processing a. Greater freedom in the selection eeeiiineier ι- · ^ uns ^r Smiuej or LösunpsnntejecmiFCi'- f-vn * - v - Example] It is first prepared in a known manner by alkaline condensation of 750 parts by weight of ßö ^ Voigem formaldehyde with 183 parts by weight of melamine in the presence of 570 parts by weight of n-butanol, a precondensate in which the melamine is present as hexamethylolmelamine. From this solution, about half of the water present is first removed in the alkaline range by circular distillation with recycling of the n-butanol. By further heating in the acidic range, the methylol compounds of melamine are etherified with n-butanol in a likewise known manner, and at the same time the condensation to a resin is effected. The residual water still present from the formaldehyde and the water additionally formed during the etherification or resin formation are removed while continuing the circular distillation. The melamine resin solution with a solids content of about 53 vol. In 1-butanol obtained after dehydration is reduced to about 7 to 78 * / o resin content by vacuum distillation and by adding: an appropriate amount of toluene or xylene or a mixture of both to δΟ ^ / ο Resin content adjusted Such a solution can be liquefied with undissolved, possibly liquefied by moderate heating Modified oil-rich or low-oil alkyd resins η the most preferred ratio of 30 to 40 Divide solid melamine resin (equal to 54.5 to 3.3 parts by weight of 55Vaiger solution) at 70 to 60 Mix the alkyd resin by weight until homogeneous. This mixture can then be used within the framework of tolerability additionally with solvents or solvent mixtures? .υι άκ · necessary for rubbing with pigments ■ ^ {- y /. ν- ν ■ .Virejcj'- or SjDrnzvisj _v Sttiit zur \ envoK 'uni: as high-quality stoving enamels are thinned. . At game 2 Instead of n-butanol as in Example 1, the same amount of i-butanol is used to produce a synthetic resin which is otherwise composed of the same amounts of melamine and formaldehyde and condensed by the same known process. The melamine resin solution obtained after dehydration has; has a solids content of about 51 to 53 ^ϋ / α in i-butanol and is thickened by vacuum distillation to about 50% resin content. Then as much toluene, xylene or a mixture of both or other aromatics are added and the melamine resin solution is adjusted to about δΟ ^ / ο solids content. As mentioned in Example 1, such a solution can be further mixed with oil-modified alkyd resins and processed onto stoving enamels. Claim: Process for the production of stoving enamels based on etherified melamine resins and oil-modified alkyd resins, characterized in that following the in the presence an alcohol carried out condensation of the melamine resin a part of the alcohol in a suitable Way removed and replaced by aromatic solvents and that the solvent-free Alkyd resin is mixed with the solution thus obtained. References considered: U.S. Patent No. 2,218,474. © 909 628/391 9.59